At present, processes related to mobility of a terminal device include cell selection and cell reselection. In the prior art, when the terminal device is switched on or enters a signal coverage area from a coverage hole, if the terminal device does not store information about a cell on which the terminal device camps before the terminal device is switched on or enters the signal coverage area from the coverage hole, the terminal device first scans all available radio frequency channels, and searches on a carrier of each radio frequency channel for only a cell having best radio frequency channel quality, and then the terminal device measures a communication parameter value of the cell, receives a broadcast message sent by a base station, and determines, according to a criterion S (select), whether the cell found by the terminal device is a suitable cell for the terminal device to camp on. When the communication parameter value obtained by the terminal device through measurement meets the criterion S, the terminal device sets the cell as a serving cell of the terminal device. A communication parameter is received signal strength or received signal quality. It should be noted that, when the terminal device sets the cell as the serving cell of the terminal device, a communication state of the cell is a non-barred state, and a barred state of the cell is a state in which the cell can only provide an emergency call communications service to the terminal device.
After the terminal device camps on the serving cell, if the broadcast message received by the terminal device includes a neighboring cell of the serving cell and a priority of the neighboring cell is higher than a priority of the serving cell, the terminal device measures the neighboring cell. If received signal strength of the neighboring cell is higher than a preset threshold of the neighboring cell in the broadcast message within a cell reselection time, the neighboring cell is used as a target cell in cell reselection of the terminal device, and the terminal device reselects the target cell.
If the priority of the neighboring cell is equal to the priority of the serving cell and received signal strength of the serving cell is less than Snonintrasearch in the broadcast message, the terminal device measures the neighboring cell. If the neighboring cell meets the criterion S and a criterion R (Reselect, reselect), the neighboring cell is used as a target cell in cell reselection of the terminal device, and the terminal device reselects the target cell. The criterion R is Rn>Rs, where Rs=Qmeas,s+QHyst, and Rn=Qmeas,n−Qoffset, QHyst is a hysteresis of the received signal strength of the serving cell, Qoffset is an offset of the received signal strength of the neighboring cell, and QHyst and Qoffset are used to prevent a ping-pong effect during cell reselection.
If the priority of the neighboring cell is lower than the priority of the serving cell, the received signal strength of the neighboring cell is less than Threshserving,low in the broadcast message, and the received signal strength of the serving cell is greater than Threshx,low in the broadcast message, the neighboring cell is used as a target cell in cell reselection of the terminal device, and the terminal device reselects the target cell.
However, when the terminal device is in a building or a basement, a signal sent by the base station to the terminal device is diffracted, reflected, or the like by an obstacle, a loss may occur in the signal that encounters the obstacle and that is received by the terminal device. Therefore, when the terminal device is in an idle state, a received signal communication parameter value obtained through measurement is relatively low, requirements of existing cell selection and cell reselection cannot be met, and the terminal device cannot communicate normally.